var dest = new String("");

    var src = new String("aze");

    var ar = new Array();

    ...

    ar.push(src);

    ar.push(src);

    ...

    dest = ar.join("");

var str1 = "Hello ";

var str2 = "world!";

var res = str1.concat(str2);

// does not change the existing strings, but

// returns a new string containing the text

// of the joined strings.

var str1 = "Hello ";

var str2 = "world!";

var res = str1.concat(str2);

console.log(res);

var str = 'Hello' + ' ' + 'world!'; // str = 'Hello world!'

// a comma ',' is the default delimiter for array.join 

var str = ['Hello',' ','world!'].join();   // str = 'Hello, ,world!'

var str = ['Hello',' ','world!'].join(''); // str = 'Hello world!'

​

var str1 = 'Hello';

var str2 = str1.concat(' ','world!');  // str1 = 'Hello', str2 = 'Hello world!"

​

var str1 = 'Hello';                    

var str2 = `${str1} world!`;           // str1 = 'Hello', str2 = 'Hello world!"

                                       // note backticks `

//This method adds two or more strings and returns a new single string.

​

let str1 = new String( "This is string one" ); 

let str2 = new String( "This is string two" ); 

let str3 = str1.concat(str2.toString());

console.log("str1 + str2 : "+str3)

​

output:

str1 + str2 : This is string oneThis is string two

const str1 = 'Hello';

const str2 = 'World';

​

console.log(str1.concat(' ', str2));

// expected output: "Hello World"

​

console.log(str2.concat(', ', str1));

// expected output: "World, Hello"

let first_string = 'I am a programmer, ';

let second_string = 'I am indisposable.';

let what_i_said  = first_string + second_string;

console.log(what_i_said);

​

/* OR 

*/

​

let tell_my_boss = first_string.concat(second_string);

console.log(tell_my_boss);

const str1 = 'Hello';

const str2 = 'World';

​

console.log(str1 + str2);

>> HelloWorld

​

console.log(str1 + ' ' + str2);

>> Hello World

// the fastest way to string concat in cycle when number of string is less than 1e6

// see https://medium.com/@devchache/the-performance-of-javascript-string-concat-e52466ca2b3a

// see https://www.javaer101.com/en/article/2631962.html

function concat(arr) {

    let str = '';

    for (let i = 0; i < arr.length; i++) {

        str += arr[i];

    }

​

    return str;

}

​